RS485/422/232 to single-mode fiber converters Manual 

      The distance and speed of optical fiber transmission aren’t related. Serial-interface fiber transmission resolves the contradiction of copper transmission’s long-distance and high-speed communications because of it’s advantages such as high reliability, security and confidentiality and so on. The use of fiber as communication transmission medium completely solves the problems such as electromagnetic interference, ground loop interference and lightning damage. It has been used more and more in industrial automation, distributed data acquisition, intelligent transportation, electricity, water, banking and many other areas and become the preferred option for communications transmission.

      FIB-485A-S is an industrial grade RS485/422/232 to fiber converter of Fourstar. It achieves RS485, RS422 or RS232(TXD、RXD、GND)signal’s transparent transmission on fiber, without changing the original communication protocols and software, plug and play, and directly replace copper Conductor transmission.

Product characteristics and major technical indicators

● voltage: 9 ~ 40 VDC wide-voltage power supply or 5 VDC power supply optional, isolate signal interface with external power within the product through DC / DC isolation module. Power consumption: <1 W

 ● interface: RS232: DTE standard interface of DB9M pin-socket, use TXD, RXD, GND lanes, with ± 15kV ESD protection and  surge protection

RS485: D +, D-  connector, with 500 W TVS Lightning Protection and ± 15kV ESD protection

RS422: TXD +, TXD-, RXD +, RXD- connector, with ± 15kV ESD protection and surge protection

● communication rate: RS232:0 ~ 230 Kbps Adaptive;RS485/422:0~500Kbps Adaptive

● applicable fiber: single-mode 9/125、10/125、8.3/125um

● wavelength: 1310 nm

● power of launched light: -6 dBm

● receiving sensitivity: -22 dBm

● transmission distance: 0 ~ 20km

(Maximum to 60 km or 120 km, 、 a statement is needed, with the standard FC connector)

● fiber interface: standard ST connector, SC and FC connector optional

● temperature: -40 ~ +85 ℃

● Relative Humidity: 0 to 95 percent (not condensed)

● Dimensions: 85 × 55 × 25 (L × W × H), the standard rails installation with bolts hole

● Weight: 100 g

The structure and shape of products:

The signal rank of DB9M neilsbed and RS232 socket

Pin number





Not be used



RS232 signal receive



RS232 signal send



Not be used,to short with 6



RS232 signal ground



Not be used,to short with 4



Not be used,to short with 8



Not be used,to short with 7



Not be used


 The signal rank of RS485/422connection terminal 

Terminal signal-name



RS485 signal positive


RS485 signal negative


RS422 signal sending positive


RS422 signal sending negative


RS422 signal receiving positive


RS422 signal receiving negative


RS485/422 signal ground


Shielding ground(chassis)




Indicator light:

PWR         power            red      always shine

TXD         data sending     yellow   twinkle when sending data to fiber

RXD         data receiving   green    twinkle when receiving data from fiber

FIB          break off      red      be lighten when the fiber is broken

      There is a LED indicator FIB besides the fiber connector Rx. When the fiber is broken, the fiber is not connected or the opposite party’s fiber converters is turn off, FIB will be lit by receiving the matt signal, witch is very convenient to judge where the fault is.

      External power: the right terminal is a two-group external power terminal, one is 9 ~ 40 VDC wide-voltage, and the other is 5 VDC fixed voltage. Any one of them is ok. You needn’t to worry about the power fluctuations. Isolating signal interface with external power within the product through DC / DC isolation module. Thus the power supply can be taken from any power terminals of equipment or powers of different equipments, to avoid the ground loop interference caused by the ground of external power and RS485/422/232 signal, and generate the safety of equipment.

Connection of RS485/422/232

      Link of RS232:For the RS232 interfaces with standard DTE way such as computer, you can directly use the RS232 socket with the product witch connect RS232 cable to fiber converters. For RS232 interfaces of non-DTE way (such as some industrial equipment’s RS232 interface), users need a self-made cable to connect the fiber converter and RS232 interfaces of equipment, and the connectivity principles are: connect sending to receiving, receiving to sending, ground to ground. Determine whether short the unused signal as the equipment’s introduction book. RS232 cable’s length can not be over 15 m.

      RS485’s connection: Connect the D + terminal of fiber converters to the RS485 interface’s positive signal of equipment, D- to RS485’s negative signal of equipment, when the distance is over 50 m, a 120 Ohm terminals resistance  need to be parallel connected between D + and D- and the RS485 terminals of equipments apiece.

      The allowed greatest cable length of RS485/422 at different baud rates :2000m(9.6Kbps)、1.5km(19.2Kbps)、1.2km(115.2Kbps)、800m(187.5Kbps)、200m(500Kbps)。

      The positive and negative signs of some equipment’s RS485/422 interface are marked as B negative and A positive (such as Mitsubishi PLC), some are marked as A negative and B positive (such as Siemens, Omron PLC), Please pay attention when connecting..

    The RS232, RS485, RS422 of this fiber converter can not communicate with each other, only one of them can be used

      The use of the RS232, RS485, RS422 of this fiber converter is without the switch or the jumper switches, the direct use is very convenient

      Use fiber to link the two fiber converters. Connect Tx to the other one's Rx, Rx to the other one’s Tx.  The bend radius when laying the fiber can’t be less than the allowed one, or the core is easily broken.

      Please pay attention to maintaining the clean of fiber’s interface socket. Please  use the configured rubber to cover it when it isn’t connected.

Typical applications map

The RS485/422/232 point-to-point communication mode composed by FIB-485A fiber converters


Connect two different zones’ RS485/422 buses by FIB-485A fiber converters

RS485/422 star network (fiber HUB) composed by FIB-485A fiber converters


Fiber repeaters and fiber mode converters composed by FIB-485A